The Nolli map was based on Bufalini’s map of 1551, with which Nolli readily invited comparison, but Nolli made a number of important innovations. Firstly, Nolli reorients the city from east (which was conventional at the time) to magnetic north, reflecting Nolli’s reliance on the compass to get a bearing on the city’s topography. Secondly, though he follows Bufalini in using a figure-ground representation of built space with blocks and building shaded in a dark pochÃ©, Nolli represents enclosed public spaces such as the collonades in St. Peter’s Square and the Pantheon as open civic spaces. Finally, the map was a significant improvement in accuracy, even noting the asymmetry of the Spanish Steps. The map was used in government planning for the city of Rome until the 1970s.
A high res (understatement when you see the map) version of the map can be found here.